1. Field of the Invention
The present invention relates generally to compressor wheels for turbochargers. More particularly, a compressor wheel is provided with an interference fitted insert in the hub sized to create a predetermined pre-stress in the hub to reduce radial rotational stress during operation of the compressor in the turbocharger. The pre-stress will also reduce the difference between the peak and minimum circumferential stress values during transient operation.
2. Description of the Prior Art
Threaded-bore and through-bore compressor wheels typically have high bore stresses at the high rotational speeds present in operation of a turbocharger. Reduction of the radial component of the bore stresses and the difference between the peak and minimum circumferential stresses during transient operation will increase the life and operating speed for compressor wheels. Additionally, through bore compressor wheels have typically employed a securing nut which does not provide optimum aerodynamic performance of the wheel. A streamlined nose design is desirable to reduce the flow disturbance at the inlet hub and hence increase the performance efficiency.
The present invention provides a compressor wheel configuration and assembly process which results in high compressive stresses of a predetermined value near the bore after wheel assembly. During rotation of the wheel in operation, the stresses transition from compression to tension, and only then to the required tensile stress inducing failure, instead of going from zero stress to high tensile stresses as in the normal throughbore wheels. The stress variation of the circumferential stress during transient operation is also reduced. This increases the wheel operating speed and life.